The present invention relates to a method for producing gear wheels from blanks obtained by sintering metal powders.
Gear wheels obtained from sintered metal powders are already known.
In particular, GB-1,125,952 discloses a method for producing gear wheels from sintered metal powders which entails, after forming a blank by sintering, the rolling of the teeth in order to give the correct size to the profiles.
Blanks with straight teeth are obtained in simple dies by pressing and sintering, while blanks with helical teeth are formed in more complex dies with a profile which is already spiral-shaped.
Rolling is then performed with complementarily shaped toothed rollers, provided with straight teeth in the former case and with helical teeth in the latter case, in order to give the correct size to the teeth, as mentioned.
Moreover, it is known from EP-552,272 to provide gear wheels by means of sintering and subsequent rolling.
The latter step is aimed at compressing the outer surface of the teeth in order to harden it and make the gear wheels adapted for power transmission instead of low-stress transmission applications.
Also in this case, the blank obtained by sintering has teeth in their final configuration, albeit with enlarged dimensions, which must be subjected to compression.
Currently, therefore, it is believed that after formation by sintering, i.e., compaction of metal powders and subsequent heating in an oven, it is possible to obtain gear wheels only by means of rolling operations which give the correct dimensions to the profile of the teeth or compress the profile in order to harden it.
After formation by sintering, the profile of the teeth already has the final shape, but its dimensions are larger than in the final product.
The aim of the present invention is to provide a method which allows to provide gear wheels from blanks obtained by sintering metal powders and allows to correct the longitudinal profile of the teeth.
Within the scope of the this aim, an object of the present invention is to provide a method which allows to produce gear wheels with tooth corrections similar to those having a ground profile starting from straight-tooth blanks.
This aim, this object and others which will become better apparent hereinafter are achieved by a method for producing gear wheels from blanks obtained by sintering metal powders, which comprises the step of:
coining longitudinal and transverse profiles of teeth of a blank with straight or helical teeth with a rolling operation by means of one or more rollers shaped complementarily to said blank with a profile which is adapted to produce modifications of said longitudinal and transverse profiles.